The research plan is for the continued development and evaluation of a miniature, mechanically rugged, simple, inexpensive, minimally invasive, electrochemical oxygen sensor. It is intended for insertion in flap or free muscle transplants after reconstructive surgery and will monitor oxygen for up to five days. An outer sheath controls the operating environment of the sensor and a membrane excludes large molecules that would contaminate the electrodes. The measurement cycle is designed to avoid interference from smaller species. Dimensions and processes expected to affect the accuracy or stability of the device will be systematically evaluated and final process and material specifications and tolerances established. Special tooling and equipment will be designed and built to improve reproducibility and reduce fabrication costs. Screening methods will be developed to reject defective components and to provide feedback on processes for improved yields. Devices will be tested extensively in the laboratory for accuracy, stability, and response time. Evaluation protocols will include sterilization and storage. Short term performance will be evaluated in rabbit tissue flaps with active manipulation of blood supply. Long term stability will be evaluated in rabbits with flaps or free tissue transfers. All animal studies will include a second sensor in intact or less disturbed tissue. Indicated oxygen level will be compared with venous oxygen levels, clinical indications of poor perfusion, and degree of transfer necrosis. Tissue from the long term animals will examined for adverse foreign body reactions to the device. PROPOSED COMMERCIAL APPLICATIONS: The device will be used to permit direct monitoring of tissue oxygenation after grafting during reconstructive surgery and provide early warning of clotting of blood vessels. It addresses limitations of existing devices and provides clinically relevant data not presently available. It is expected to capture a significant portion of a market estimated at $8,000,000 in the US.